Pumps for pumping coolant around automotive engines are typically mechanically driven via a direct mechanical connection with an output shaft of the engine which the pump is intended to cool. It will be appreciated that when a pump is driven in this way, there is a direct correlation between the speed of the engine and the speed of operation of the pump. However, it may be desirable to control the speed of the pump independently of the engine speed, and in order to do this, it is known to connect the pump to the engine output shaft via a magnetic coupling.
Such couplings generally include a part which includes a magnetic element and another part which includes an electrically conductive material, the two parts being moveable relative to one another. One part of the coupling is connected to and driven by an engine output shaft, for example, by a pulley, and the amount of torque transmitted from the engine output shaft to the pump depends upon the proximity of the magnetic element to the electrically conductive material. The greater the gap between the magnetic element and the conductive material, the smaller the proportion of engine output torque is transmitted to the pump.
It is known to actuate the relative movement of the two parts of such couplings mechanically for example by means of a lever. A challenge of such couplings is that a substantial distance in an axial direction of the coupling may be required between the two parts of the coupling and the connection to the engine output shaft, in order to accommodate the lever.
Furthermore, the actuator should not obstruct any part of the engine assembly.
The actuator (i.e. lever) is usually contained within a housing which should be sealed to avoid debris from entering the coupling. Providing a suitable and effective seal for sealing the housing can be problematic, as such seals are often awkward and vulnerable to damage.